PDF does not display from media library

I have several pdf's that have been uploaded to my media library. They no longer display when I link to them on my WP site pages. Clicking on the link appears to connect (the correct url displays in the browser), but the page that is displayed in the browser is blank. I've tried in both Firefox and Safari, same result. No problem with other file types (jpg, doc).
I have not had a problem with this in the past, could it be WP? I recently updated to 3.4.2.

I’m sorry but you have posted to the wrong support forum. We cannot help you here at WordPress.com with that site as it’s not being hosted by WordPress.com and we run on different software. This is the correct forum for your software http://wordpress.ORG/support/ If you have not registered a WordPress.org username account yet you can do so on the top right hand corner of the page I just linked to so you can post to those support forums.
WordPress.com vs WordPress.org: The Differenceshttp://support.wordpress.com/com-vs-org/
Best wishes with your site.